Molecular tension authenticates apoptotic cells being phagocytosed

Profound cytoskeletal reorganization and plasma membrane deformation in phagocytes is indispensable for phagocytosis of massive apoptotic cells, but whether these dynamics accompany a mechanical signal modulating signaling during efferocytosis remains largely unexplored. Here, we report that tension between phosphatidylserine (PS) and PS receptors (PSR) generated at the phagocytic synapse serves as a signal to determine whether PS-exposing cells should be phagocytosed. Mechanistically, increased membrane tension of phagocytes via Rac1-dependent actin polymerization and membrane stiffness of apoptotic cells caused tension between PS and PSRs, leading to phosphoinositide 3-kinase recruitment to PSRs, which resulted in Rac1 inactivation and myosin II phosphorylation required for phagocytic cup closure. Our observations imply that tension between PS and PSRs acts as a mechanical fail-safe to prevent removal of all PS-exposing cells for the integrity of efferocytosis.